The present invention relates to packaging materials and particularly to packaging materials for packaging foodstuffs and more particularly to packaging with packaging materials having a food grade coating, particularly a food grade barrier coating.
The coating of substrates with food grade films is already known. Japanese Kokai JP-A-54-95749 describes a packing coating based on soybean protein and other proteins. There are several problems with this type of coating. First, the need to use several types of protein makes it more difficult and more expensive to manufacture this kind of coating. Further, the use of soybean protein, in particular, has several drawbacks, in that, firstly a coating solution based on soybean protein takes some time to dry to form a coating; secondly, the mechanical and thermal properties of soy protein-based coatings are rather poor and the coating is not transparent; and thirdly, this type of coating must be bound to a specific type of in that, to obtain proper adhesion, the substrate must be a synthetic resin which is active to soybean protein.
Japanese Kokai JP-A-3-198754 describes a type of substrate coating for food and drug packing which is water-proof. However it is only water-proof at room temperature or slightly above. According to this patent, the film is thermally soluble and dissolves in 3 to 5 min. at 60 to 70.degree. C. if it is in contact with water. Furthermore, the film appears to have rather poor mechanical properties since a three-layer structure is required to ensure acceptable physical strength. Also the film contains, among other components, pullulan which is not approved for food use either in Europe or in the United States of America.
Therefore, there is a need for a packaging material having a food grade coating which is water and fat resistant, having good mechanical properties and is relatively simple to produce.